Method and apparatus for production of helical springs by spring winding

ABSTRACT

A method produces helical springs by spring winding with a numerically controlled spring winding machine, a wire is fed, controlled by an NC control program, through a feed device to a forming device of the spring winding machine and is formed with the aid of tools in the forming device to form a helical spring. A measurement time is defined which occurs in a final phase of an overall manufacturing time for the helical spring at a time period before the end of the overall manufacturing time. A position of a spring end which is formed by an end surface of the wire is measured at this measurement time to determine an actual angle position of the spring end. A remaining distance for the wire feed is then calculated to achieve a nominal angle position of the spring end, as intended for the helical spring, at a reference time which occurs at a later time and the wire is fed through the remaining distance. The method allows the relative angle position of the spring ends of a helical spring to be set very precisely.

RELATED APPLICATION

This application claims priority of German Patent Application No. 102010 014 386.3, filed on Apr. 6, 2010, the subject matter of which isincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to methods for production of helical springs byspring winding with a numerically controlled spring winding machine, andto spring winding machines suitable for carrying out the method.

BACKGROUND

Helical springs (also denoted as coil springs) are machine elementsrequired in large quantities and different configurations in numerousfields of application. Helical springs, which are also referred to aswound torsion springs, are normally produced from spring wire and are inthe form of tension springs or compression springs depending on theirload during use. Compression springs, in particular bearing springs, arerequired, for example, in large quantities for automobile construction.The spring characteristic can be influenced, inter alia, by sections ofdifferent pitch or with different pitch profiles. For example, in thecase of compression springs, there is frequently a central section ofgreater or lesser length with a constant pitch (constant section)adjacent to which, at both ends of the spring, there are contact areaswith a pitch which becomes less towards the ends. In the case ofcylindrical helical springs, the spring diameter is constant over thelength of the springs, but it may also vary over the length, forexample, in the case of conical or barrel-shaped helical springs. Inaddition, the overall length of the (unloaded) spring may vary widelyfor different applications.

Nowadays, helical springs are normally produced by spring winding withthe aid of numerically controlled spring winding machines. In this case,a wire (spring wire) is fed, controlled by an NC control program, by afeed device to a forming device of the spring winding machine, andformed with the aid of tools of the forming device, to form a helicalspring. The tools generally include one or more variable-positionwinding pins to fix and possibly to vary the diameter of spring turnsand one or more pitch tools which govern the local pitch of the springturns in each phase of the manufacturing process.

Spring winding machines are generally intended to produce a large numberof springs with a specific spring geometry (nominal geometry) withinvery narrow tolerances, at a high rate. The functionally importantgeometry parameters include, inter alia, the relative angle position ofthe spring ends at the opposite end areas of the helical spring. In thiscontext, the term “spring end” denotes the end surface of the wire whichforms the helical spring, which end surface is produced by a shearingprocess. Errors in the relative angle position of the spring ends canlead to errors in the block size (length in the completely compressedstate), in the spring length of the unloaded spring, in the spring forceand in the grinding pattern of the spring end faces.

To comply with stringent quality requirements, for example, in theautomobile field, it is normal practice to measure certain springgeometry data, for example, the diameter, length, pitch, and/or pitchprofile of the spring, and/or the relative angle position of the springends at both ends of the helical spring after completion of a spring andto automatically sort the finished springs depending on the result ofthe measurement, into satisfactory parts (spring geometry within thetolerances) and unsatisfactory parts (result outside the tolerances),and possibly into further categories. This procedure is highlyuneconomic, in particular in the case of long springs since, in the caseof long springs, a relatively great length of wire is consumed for eachspring and must be thrown away if it is found that the finished springis outside the tolerances.

It has already been proposed for the diameter, length and pitch of thespring to be checked by suitable measurement means during manufacture,and for manufacturing parameters to be changed in the event of anydiscrepancies outside tolerance limits such that the spring geometryremains within the tolerances. DE 103 45 445 B4 discloses a springwinding machine which has an integrated measurement system with a videocamera which is directed at that area of the spring winding machine inwhich the forming of the spring starts. An image processing systemconnected to the video camera and having appropriate evaluationalgorithms is intended to allow the diameter, length and pitch of thespring to be checked during manufacture, and it is intended to bepossible to vary these spring geometry parameters by feedback to theprocessing tools, which can be adjusted by motors, during manufacture.An evaluation algorithm for determining the current spring diameter isdescribed in detail.

The relative angle position or angular position of the spring ends withrespect to one another can also fluctuate greatly as a function ofmaterial characteristics of the wire and of the geometry of the spring.One known method for limiting severe scatters in the relative angleposition uses a measurement probe which produces a measurement signalwhen the front spring end (that which is produced firstly) of thedeveloping spring reaches a specific position at a time before the endof the overall manufacturing time, the angular distance of which (alongthe turns) to the desired nominal angle position at the end of the totalmanufacturing time is known. There is a defined remaining distancebetween the response position of the measurement probe, which themeasurement system knows in advance, and the nominal position of thespring end which is desired at the end of the manufacturing process,measured along the profile of the turns, and this remaining distance isconstant for all helical springs for the manufacturing process that hasbeen set out. The wire feed control is programmed such that a wire feedwhich is taking place is interrupted when the measurement proberesponds, and the preprogrammed constant remaining distance at the wirefeed is then also moved through, as a result of which the spring endthen reaches the desired nominal angle position. Mechanical measurementprobes with a variable stop and optical measurement probes have alreadybeen used, which use a laser to determine that the monitored angleposition at the spring end has been reached. Measurement systems withmeasurement probes such as these generally have a complex design.

It could therefore be helpful to provide a method and an apparatus of ageneric type such that, particularly when producing relatively longhelical springs, helical springs can be produced within tight geometrictolerances with high reliability, composed of wire materials of widelydiffering quality. It could also be helpful to provide for theproduction of long helical springs with little scatter of the relativeangle position of the spring ends.

SUMMARY

We provide methods of producing helical springs by spring winding with anumerically controlled spring winding machine including feeding a wirecontrolled by an NC control program through a feed device to a formingdevice, forming the wire into a helical spring in the forming device,defining a measurement time which occurs in a final phase of an overallmanufacturing time for the helical spring at a time period before theend of the overall manufacturing time, measuring a position of a springend formed by an end surface of the wire to determine an actual angleposition of the spring end at the measurement time, determining aremaining distance for the wire feed required to achieve a nominal angleposition of the spring end, as intended for the helical spring, at apredefined reference time which occurs at a time after the measurementtime, and feeding the wire through the remaining distance.

We further provide spring winding machines that produce helical springsby spring winding under the control of an NC control program including afeed device and a forming device that receives wire from the feed deviceand includes at least one winding tool which controls diameter of thehelical spring at a predeterminable position, and at least one pitchtool whose action on a helical spring being produced controls a localpitch of the helical spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic overview illustration of one example of aspring winding machine with parts of the feed device and of the formingdevice.

FIG. 2 shows a perspective illustration of fittings for the springwinding machine as shown in FIG. 1 including two cameras of acamera-based, optical measurement system for contactless real-timerecording of data relating to the geometry of a spring which iscurrently being produced, and a spring guide device.

FIG. 3 shows the situation illustrated in FIG. 2 viewed from a directionparallel to the optical axis of the camera optics of the second camera.

FIG. 4 shows an enlarged illustration of a detail of the field of viewof the second camera when the actual angle position of the spring end isbeing measured at a measurement time before the end of manufacture.

FIG. 5 shows an enlarged illustration of a detail of the field of viewof the second camera when the spring length is being measured at ameasurement time after the end of manufacture.

FIG. 6 schematically illustrates an axial view of the free spring endsection of a helical spring to explain a correction method fordetermining the actual angle position of the spring end.

FIG. 7 shows a calculation scheme for determining the sought arc lengthbe in the course of the correction method.

DETAILED DESCRIPTION

It will be appreciated that the following description is intended torefer to specific examples of structure selected for illustration in thedrawings and is not intended to define or limit the disclosure, otherthan in the appended claims.

We provide methods for production of helical springs by spring windingwith a numerically controlled spring winding machine, the methodcomprising:

-   -   feeding a wire controlled by an NC control program through a        feed device to a forming device of the spring winding machine;        and    -   forming the wire into a helical spring with the aid of tools in        the forming device;    -   defining a measurement time which occurs in a final phase of an        overall manufacturing time for the helical spring at a time        period before the end of the overall manufacturing time;    -   measuring a position of a spring end, which is formed by an end        surface of the wire, to determine an actual angle position of        the spring end at the measurement time;    -   calculating a remaining distance for the wire feed required to        achieve a nominal angle position of the spring end, as intended        for the helical spring, at a predefined reference time which        occurs at a time after the measurement time; and    -   feeding the wire through the remaining distance.

There is also provided a spring winding machine configured to performthe method.

In the method, a measurement time is defined which occurs in the finalphase of the overall manufacturing time required for the manufacture ofa complete helical spring at a time period before the end of the overallmanufacturing time of the individual spring, that is to say at a timebefore the end of the process of manufacturing a spring. At themeasurement time, the position of the spring end, which is defined bythe end surface of the wire, is measured to determine an actual positionof the spring end at the measurement time. A remaining distance iscalculated on the basis of the result of this measurement through whichthe wire still has to be fed or fed forward with the aid of the feeddevice until a nominal angle position of the spring end, which ispredetermined for the helical spring, is reached at a predefinedreference time which occurs at a time after the measurement time. Thewire is then fed forward with the aid of the control system through thiscalculated remaining distance.

The reference time may correspond to the end of the overallmanufacturing time. In these cases, the opposite spring end can beproduced immediately when the reference time is reached in that acutting device is used to separate the helical spring that has beenproduced from the fed wire. This is generally provided when only aconstant section, that is to say a section with a constant pitch,without any pitch change is manufactured after the reference time beforethe spring is cut off from the wire, that is to say for an open springend section.

The reference time may also be an intermediate time which occurs at atime before the end of the overall manufacturing time. This is generallyused when an end section with a pitch change is also manufactured afterthe reference time, in particular a contact section with a pitch whichdecreases to the spring end to create an end with touching turns. Thus,in this case, the movement through the remaining distance is alsofollowed by a final part of greater or lesser duration of themanufacturing time. This final part is specific for the spring geometryof one spring batch and is preset as being fixed in the control programand is, therefore, constant. The final part is normally sufficientlyshort in comparison to the overall manufacturing time that no orscarcely any angle position errors can build up.

Depending on the length of the spring, there is in any case a remainingtime between the measurement time and the end of manufacture which, forexample, may be more than about 5%, more than about 10%, more than about20% or more than about 30% of the overall manufacturing time.

The term “time” in this application means a specific point within the NCcontrol program, that is to say a program time or a time within theprogram sequence. A “time period” is correspondingly a period betweenprogram times of a program-time function. To this extent, a program timecorresponds to a sequence position in the sequential process of programsteps while the program is being processed. For example, if a triggersignal is required to operate a measurement device in a specific phaseof processing the program, this trigger signal can be triggered by aprogram line that occurs at an appropriate point. This allows a“measurement time” to be defined in the program. In the program, signalssuch as these are directly linked to specific positions of the machineaxes, for example, to the machine axis of the wire feed and/or to themachine axis for the position of the pitch tool. A “time” in aprogram-time function therefore corresponds to a point on the movementcurve of one or more machine axes. A program-time function results intimes (program times) within an NC program synchronized to the progressof the spring production. To this extent, the program-time function isalso a movement function with respect to the movements of machine axes.In particular, a program-time function also corresponds to a movementfunction of the wire feed.

In the prior art methods, the response position of a measurement probepredetermines a location of the observed spring end, and a constantremaining distance is moved through starting from this location. In ourmethods, a measurement time is predetermined and a remaining distancefor the remaining forward feed results in a variable form andindividually for each spring as a function of the angle position of thespring end detected at the measurement time, which is referred to as the“actual angle position.”

With respect to the control program, the difference can be described bystating that, in conventional methods, the time of response of themeasurement probe with respect to a position in the NC control programis variable, but the remaining distance is constant. In contrast, in ourmethods, the position at the measurement time is constant orpredetermined in a fixed manner in the NC control program, while incontrast, the remaining distance is variable and results individuallyfor each spring only from the calculation on the basis of the measuredactual angle position, or the actual angle position derived from themeasurement.

There is no need for optical or mechanical measurement probes of complexdesign. We also avoid the adjustment effort associated with the use ofsuch devices, thus considerably simplifying the handling. Somemeasurement probes are also susceptible to defects. In the case of thinwires, electromechanical probes, for example, are occasionally used,which close an electrical circuit by touching contact when they touchthe spring end. We avoid the contact problems occasionally observed inthis case.

Preferably, a camera with a two-dimensional field of view is used formeasurement and the camera arranged such that the end section of thespring with the spring end lies within the field of view at themeasurement time. Measured values can then be determined with the aid ofan image processing system associated with the camera. Some conventionalspring winding machines already have suitable measurement cameras tomeasure the overall length of the finished spring, its diameter and/orother geometric data which can be defined in the end area of the springafter the end of manufacture. It may be possible to use these camerasfor a new measurement task. This makes it possible to save the designcomplexity required for conventional measurement probes.

The measurement can also be carried out by other measurement means. Byway of example, a laser system can be used for measurement.

An arrangement of the camera with the observation direction in thelongitudinal direction of the spring is possible to record and evaluateimages of the end face of the helical spring with the spring end.However, this may obstruct the operation of the spring winding machine.Inter alia, it is therefore preferable for the camera to be arrangedalongside the position in which the helical spring can be expected oralongside the movement to be traveled by the helical spring, and for anobservation direction of the camera to be aligned transversely, inparticular at right angles, to the alignment of the longitudinal axis ofthe helical spring during spring manufacture. The end section with thespring end can then be recorded in a side projection, in which thespring end then normally represents a step with greater or lessercurvature, depending on the angle position.

In one method for determining the actual angle position of the springend at the measurement time, a distance value is determined for adistance, which is measured, for example, at right angles to thelongitudinal axis of the spring between a tangent to an external contourof a turn of the helical spring and a projection of the spring end inthe field of view. Since the spring end is normally displayed as aclearly defined contour with greater or lesser curvature in the sideprojection, a distance measurement such as this can be carried out usingknown distance determining tools in an image processing system with highprecision and within a short time.

In one method, which provides particularly precise measured values, arelative orientation of the spring end is determined at the measurementtime with respect to an observation direction, and the value for thedistance value is corrected as a function of the orientation. This makesit possible to take account of projection effects which can have adisadvantageous effect on the measurement accuracy, particularly whenthe wire diameter is relatively large.

The timing of the measurement time with respect to the spring geometryis preferably configured such that in a remaining time interval which isrequired to move through the remaining distance, that is to say in thetime between the measurement time and the intermediate time or the endof manufacture at least one turn of the helical spring is also produced,with the remaining time interval preferably being sufficiently long thatbetween one turn and three turns of the spring are also produced whilemoving through the remaining distance. Such remaining time intervals areon the one hand long enough to move through the calculated remainingdistances with sufficient accuracy, while on the other hand they aresufficiently short to avoid an error in the position of the spring endat the end of the manufacturing process resulting over the remainingdistance, for example, because of wire quality fluctuations.

In some of our methods, the feed movement of the wire is brieflyinterrupted to carry out the measurement such that the spring end to bemeasured is stationary at the measurement time. This allows measurementswith high measurement accuracy, and the remaining distance to be movedthrough after continuation of the feed movement can be taken intoaccount with little effort in the control of the machine. It is alsopossible to carry out the measurement while the wire is being fedcontinuously and to correct the remaining distance determined from themeasurement by a component which results between the detection of thespring end at the measurement time and the consideration of themeasurement result in the machine control system.

Preferably, at least one further measurement is carried out after theend of manufacture and before the helical spring is cut off from the fedwire. By way of example, this further measurement can be used todetermine the overall length of the finished helical spring and/or itsdiameter and/or other geometric parameters. Alternatively oradditionally, it would also be possible to use the further measurementto determine the actual angle position of the spring end at the end ofthe overall manufacturing time to check the success of the method.

Both measurements can be carried out using the same measurement means,in particular using the same camera since the position of the spring endat the measurement time which occurs before the end of manufacture, andthe position of the spring end at the end of the overall manufacturingtime are normally not far apart from one another, that is to say onlyone or a few turns.

We also provide numerically controlled spring winding machines speciallyconfigured to carry out the method. These machines have a feed devicefor feeding wire to a forming device as well as a forming device with atleast one winding tool which essentially governs the diameter of thehelical spring at a predeterminable position as well as at least onepitch tool whose action on the developing helical spring determines thelocal pitch of the helical spring.

The spring winding machine preferably has a camera positioned at adistance from the forming device such that a free spring end sectionruns into the coverage area of the camera in a final phase of theproduction of the helical spring. When using a camera with asufficiently large coverage area, the camera can be used for a pluralityof spring end measurements which can be carried out successively intime.

In some modern CNC spring winding machines which already have a suitablemeasurement system with a camera, our methods can be implemented subjectto already existing design preconditions. We provide the capability ofimplementing additional program parts or program modules, or a programchange in the control software of computer-aided control devices.

We further provide computer program products stored in particular on acomputer-readable medium or in the form of a signal, wherein thecomputer program products result in the computer carrying out ourmethods or preferably to products loaded in the memory of a suitablecomputer and run by a computer.

These and further features are disclosed not only in the appendedclaims, but also in the description and the drawings, wherein theindividual features can in each case be implemented on their own or ingroups of two or more in the form of sub-combinations and in otherfields.

Turning now to the drawings, the schematic overview illustration in FIG.1 shows major elements of a CNC spring winding machine 100 based on aknown design. The spring winding machine 100 has a feed device 110equipped with feed rollers 112 and feeds successive wire sections of awire 115 which comes from a wire supply and passes through a directingunit with a numerically controlled feed rate profile into the area of aforming device 120. The wire is formed with the aid of numericallycontrolled tools in the forming device to form a helical spring. Thetools include two winding pins 122, 124 arranged offset through an angleof 90° aligned in the radial direction with respect to the center axis118 (corresponding to the position of the desired spring axis), anddetermine the diameter of the helical spring. The position of thewinding pins can be varied for basic adjustment for the spring diameterduring the setting-up process along the movement lines shown bydashed-dotted lines and in the horizontal direction (parallel to thedirection in which the wire is introduced) to set the machine up fordifferent spring diameters. These movements can also be carried out withthe aid of suitable electrical drives monitored by the numerical controlsystem.

A pitch tool 130 has a tip aligned essentially at right angles to thespring axis and engages in the developing spring alongside the turns.The pitch tool can be moved with the aid of a numerically controlledmovement drive for the corresponding machine axis parallel to the axis118 of the developing spring (that is to say at right angles to theplane of the drawing). The wire which is fed forward during springproduction is forced in a direction parallel to the spring axis by thepitch tool corresponding to the position of the pitch tool, with thelocal pitch of the spring in the corresponding section being governed bythe position of the pitch tool. Pitch changes are produced by moving thepitch tool parallel to the axis during spring production.

The forming device has a further pitch tool 140 which can be suppliedvertically from underneath and has a wedge-shaped tool tip insertedbetween adjacent turns when the pitch tool is being used. The adjustmentmovements of the pitch tool run at right angles to the feed direction.The pitch tool is not used in the illustrated production process.

A numerically controllable separating tool 150 is fitted above thespring axis and cuts the helical spring that has been produced off fromthe wire supply being fed with a vertical working movement aftercompletion of the forming operations. In FIG. 1, the wire which has beenfed is shown in a situation immediately after the previously completedhelical spring has been cut off. In this position, the wire has alreadyformed half a turn and the wire end which forms the spring start islocated 0.3 turns before the position of the pitch tool 130.

The machine axes of the CNC machine which belong to the tools arecontrolled by a computer-numerical control device 180 which has memorydevices in which control software resides including, inter alia, an NCcontrol program for the working movements of the machine axes.

To manufacture a helical spring, starting from the “spring completeposition” shown, the wire is fed in the direction of the winding pins122, 124 with the aid of the feed device 110, and is deflected by thewinding pins to the desired diameter, forming a curve in the form of acircular arc until the free wire end reaches the pitch tool 130. Whenthe wire is fed further, the axial position of the pitch tool determinesthe current local pitch of the developing helical spring. The pitch toolis moved axially under the control of the NC control program when it isintended to change the pitch during spring development. The actuatingmovements of the pitch tool essentially govern the pitch profile alongthe helical spring.

When setting up the spring winding machine, the forming tools are movedto their respective basic settings. In addition, the NC control programis created or loaded, controlling the actuating movements of the toolsduring the manufacturing process. The geometry input for the springwinding machine is carried out by an operator on the display and controlunit 170 which is connected to the control device 180.

A number of fittings which are advantageous for implementation of themethod for the spring winding machine as shown in FIG. 1 will now beexplained with reference to FIG. 2. The elements from FIG. 1 areannotated with the same reference symbols as in FIG. 1. FIG. 2 shows thespring winding machine during the production of a relatively long,cylindrical helical spring 200 of which approximately 20 turns havealready been produced at the time shown in the figure. This is a longspring with an L/D ratio between the overall length L of the completedspring and the diameter D of the spring of more than ten. To ensure thatthe spring, which becomes ever longer as the wire feed increases,remains straight and that its free end does not bend downwardly, aspring guide device 210 is provided. The spring guide device has anangle plate 212, which is attached with an approximately horizontallongitudinal axis to the frame of the spring winding machine, and has aV-shaped profile. The flat inclined surfaces of the angle plate whichrun together downward support the spring at the bottom and at the sidesuch that the longitudinal axis (central axis) of the developing springruns coaxially with respect to the center axis 118 of the developingspring. The angle plate is attached to the machine frame with a holdingdevice, which is not shown, and it can be adjusted in height and inlateral direction to allow the desired guidance, coaxial with respect tothe center axis 118 of the spring, for springs of different diameter.After completion of the process of manufacturing a spring, the angleplate can automatically be pivoted downwardly by a hydraulic pivotingdrive to allow the finished spring to slide into a collecting container.

That end of the angle plate which faces the forming device is locatedwith a clear separation of a few centimeters away from the formingdevice such that a fully floating spring section 202 remains between thetools of the forming device and the machine-side start of the angleplate. The length of the angle plate is matched to the overall length ofthe finished helical spring such that the spring end sectionmanufactured first projects freely beyond that end of the angle platewhich is remote from the machine during the final manufacturing phase.The freely floating spring section 202 close to the machine and thespring end section 204 remote from the machine are thus accessible foran optical measurement with an observation direction at right angles tothe longitudinal axis of the helical spring.

The spring winding machine is equipped with a camera-based, opticalmeasurement system for contactless real-time recording of data relatingto the geometry of a spring currently being produced. The measurementsystem has two identical CCD video cameras 250, 260 which, in theexample, with a resolution of 1024×768 pixels (image elements) cansupply up to 100 images per second (frames per second) via an interfaceto a connected image processing system. The recording of the individualimages is in each case triggered via trigger signals from the controlsystem. This defines the measurement times. The image processingsoftware is accommodated in a program module which interacts with thecontrol device 180 for the spring winding machine, or is integratedtherein.

Both cameras are mounted on a mounting rail 255 which is resistant totwisting and attached at the side to the machine frame of the springwinding machine, adjacent to the spring guide device in the area of theguide rollers of the feed device such that the longitudinal axis of themounting rail runs parallel to the machine axis 118. The measurementcameras can be moved longitudinally on the mounting rail and can befixed at any desired selectable longitudinal positions.

The first camera 250, which is close to the machine, is fitted such thatits rectangular field of view covers a part of the freely floatingspring section 202 at a distance from the forming tools.

The second camera 260 is intended to record the free spring end 204 andtherefore positioned on the mounting rail such that the free spring endruns into the coverage area of the second camera during the final phaseof production of the helical spring.

An illumination device is fitted at the height of the axis 118diametrically opposite the cameras, providing illumination in the formof a flash at the measurement times predetermined by the control systemand as a reaction to trigger signals from the control system, allowingtransmitted-light measurement. A front-lighting device can be providedon the side of the cameras to improve the visibility of interestingdetails of the spring for measurement.

FIG. 3 shows the situation illustrated in FIG. 2 from a viewingdirection parallel to the direction of the wire feed (C axis of thespring winding machine) or parallel to the optical axis of the cameraoptics of the first camera. A section through the wire 115 can be seenon the left, which is fed in the feed direction (at right angles to theplane of the drawing) to a curved inclined surface of the lower windingtool 124. The winding tool forces the wire upwardly onto a path which iscurved in a circular shape in the direction of the upper winding tool,and in the process the wire is permanently formed. The tip of the pitchtool 130 can be seen above the winding tool, and a side working surfaceof the tip rests on the developing turn. The pitch tool can be movedparallel to the spring axis 118 (in the direction of the arrow) under NCcontrol with the aid of the associated machine axis such that the localpitch of the spring at the forming location is governed by the positionof the pitch tool.

In FIG. 3, solid lines show a situation in the final phase ofmanufacture of a cylindrical helical spring 200, which has an endcontact section 206, which has already been produced, with acontinuously increasing pitch, followed by a constant section 208 with aconstant pitch and an opposite contact section, which has not yet beenmanufactured at the illustrated time, with a decreasing pitch. Themanufacturing process has not yet been completed at the illustratedtime, and some turns (for example, between 1 and 5) still need to beproduced. However, the manufacturing process has already advanced so farthat the free spring end section 204 has already passed the angle plate212 of the spring guide device and projects freely from the machine sideinto the rectangular field of view 262 of the second camera.

A smaller rectangular measurement area 264 can be seen within therectangular field of view 262 of the second camera 260, which includesthe area of the free spring end section 220 and the turn sections whichare located vertically above and below this in the image with a highpoint 224 and low point 266 which appear to be curved in a semicircularshape. The free spring end section is bounded at the end by the endsurface 222 of the wire 115. This more or less planar end surface wasproduced in a shearing process by the cutting apparatus after completionof the manufacture of the previous spring, and is also referred to inthis application as the “spring end.”

FIG. 4 shows an enlarged illustration of the situation shortly beforethe end of manufacture.

The dashed lines in FIG. 3 show the same spring at a later time aftercompletion of the overall manufacturing time, but before cutting offfrom the wire supply. The field of view of the camera is sufficientlylarge that both situations can be covered in the same field of view withthe same camera setting.

FIG. 5 shows an enlarged illustration of the situation after the end ofmanufacture. The free end section of the spring is in this case enclosedby a different rectangular measurement area 266 which can be activatedin the same field of view, but is not illustrated in FIG. 3 for clarityreasons.

The measurement areas 264 and 266 represent measurement tools in theimage processing system connected to the camera. The image content canbe analyzed with the aid of these tools, for example, to determinegeometric data.

During large-scale manufacture of helical springs, the followingprocedure can be used with this spring winding machine. First, thedesired nominal geometry of the helical spring is entered on the displayand control unit 170, or appropriate already available geometric data isloaded from a memory of the spring winding machine, for example, byinputting an identification number. A so-called “NC generator” uses thegeometric data to calculate an NC control program, whose individual NCsets and their sequence control the coordinated working movements of thedevices and tools of the spring winding machine during the subsequentmanufacturing process.

The feed device produces a wire feed at a defined feed rate. The wire isformed on the tools of the forming device to form a helical spring whichdevelops ever further. The front spring end section which is producedfirst is in this case moved ever further away from the forming toolsand, after passing through the spring guide device 210, finally entersthe field of view 262 of the second camera 260. A feed interruption isprogrammed in the NC control program at a fixed predetermined point anumber of turns before the end of manufacture, such that, for example,the feed is stopped one to five turns before the end of manufacture.This program time is chosen such that the free end section 220 of thespring on the side of the turn facing the second camera is located asfar as possible in the central area between the high points and the lowpoints of the turns. The spring end then appears as a more or lesscurved step in the projection of the image display. An image recordingis then triggered by a trigger signal in the NC program at a measurementtime, and is used as the basis for evaluation by the image processing.

The trigger signal need not come from the control program. For example,the drive unit for the wire feed may contain a position transmitterwhich produces a trigger signal at the correct position, at a desiredpoint in the wire feed.

The position of the spring end formed by the end surface 222 of the wireis determined from the image or from the image data representing theimage. In the example, an image processing measurement tool whichoperates in the form of a caliper gage is used for this purpose. In thiscase, a virtual upper limiter 272 is applied in the form of a tangentwhich runs more or less parallel to the spring axis 118 to the contourof the high point 224, and a lower limiter 274 is applied parallel tothe upper limiter in the form of a tangent to the contour of the springend. The vertical distance Y, which is represented by the double-headedarrow, between the limiters, is then stored as the measured value.

This measured value Y, which is determined in the side projection,(distance measured value) correlates directly with the angle position atthe spring end at the measurement time, that is to say with the anglewhich the spring end includes with a reference direction, whenconsidered in the axial direction of the spring, with this referencedirection running vertically (on the plane of the drawing in FIG. 3), byway of example. A remaining distance is calculated on the basis of thismeasurement of the spring end through which the wire still has to be fedwith the aid of the feed device for the spring end to be in the correctangle position with respect to the other spring end, which is producedat the opposite end with the aid of the cutting device at a laterreference time. This calculated remaining distance is then transferredto the wire feed control system and is used as the basis for the rest ofthe feed process.

Depending on the spring type, the reference time may correspond to theend of manufacture or to an intermediate time which occurs before theend of manufacture.

In the example of a spring with contact sections at both ends, anintermediate time is reached at the end of the remaining distance, whichis followed by a fixed programmed final part of the manufacture in whichthe opposite contact section is produced with a decreasing pitch, untilthe end of manufacture is reached. If the spring has an open end(constant pitch up to the spring end) at the opposite end, then theremaining distance is preferably calculated such that the end of theprocess of manufacturing the spring is reached at the end of theremaining distance.

An example of the evaluation of the measured value Y of the distancemeasurement which may be used will be explained with reference to FIGS.6 and 7. FIG. 6 schematically illustrates an axial view of the freespring end section of a helical spring in which the turns which arelocated one behind the other in the axial direction appear as a singlering. This spring is recorded from the left with the aid of the secondcamera 260. The end surface 222 of the spring is shown in two differentangle positions which will be explained later. As a result of themanufacturing process, the end surface of the spring is not at rightangles to the center line of the wire, but is inclined with respect toit. The wire length measured along the wire is represented by theexternal arc length of the wire turn, that is to say by the arc lengthradially on the outside of the turns.

The calculation of the remaining distance starts from a fictitiousremaining distance which corresponds to that remaining distance betweenthe fictitious end position 222-1 of the spring end and the desirednominal position of the spring end at the reference time. The nominalangle position may, for example, be at a remaining distance of 60 mm(corresponding to an arc length which can be determined therefrom) fromthis fictitious position of the spring end. To determine the remainingdistance which actually still needs to be fed, the evaluation processnow searches for that arc length b which corresponds to the angularinterval between the actually measured position of the spring end 222and the fictitious position 222-1 of the spring end. This arc length bcorresponds to a specific wire length. As can be seen directly from FIG.6, in the example of the spring end surface 222 which is positionedobliquely, the measured value Y does not directly correspond with thesought arc length b since the lower limiter for the distance measurementhas probed that contour which is formed by the internal radius of theturn. A situation such as this results whenever the end surface 222 canbe seen from the viewing direction of the camera.

To avoid such errors which adversely affect the measurement accuracy,the relative orientation of the spring end with respect to theobservation direction is determined at the measurement time, and thevalue for the distance value Y is corrected as a function of theorientation. For this purpose, before starting the process ofmanufacturing a batch of springs, the operator uses a referencemeasurement to determine that angle position of the spring end at whichthe end surface of the wire is precisely parallel to the observationdirection. This situation, which is annotated with the reference symbol222′, is referred to as the angle neutral position and, in the case ofthe distance measurement from the view of the second camera, wouldcorrespond to a distance value X, which can be referred to as thedistance measure for the angle neutral position. This distance measure Xis specific to the spring geometry and the type of cut.

The decision to be made by the evaluation system as to whether acorrection is or is not required for the measurement because of theoblique position of the spring end surface can be considerablysimplified by determining the angle neutral position and the associateddistance measure X for the angle neutral position. Whenever the distancemeasured value Y measured in the subsequent measurement is greater thanthe distance measure X for the angle neutral position, the correspondinglimiter of the distance measurement tool probes the external radius ofthe spring turn thus allowing the external arc length to be determinedwithout any correction from geometric relationships. In contrast, as inthe example in FIG. 6, if the measured distance value Y is less than thedistance measure X for the angle neutral position, then the end surface222 can be seen in the field of view and the internal radius of the turnis probed. This means that, if the measured value Y is less than thedistance measure X for the angle neutral position, a correction iscarried out.

FIG. 7 shows one possible calculation scheme for determining the soughtarc length b. The following parameters, which are also shown in FIG. 6,are used in this case: r_(a): external radius of the spring; r_(i):internal radius of the spring; α′: angle between the angle nulldirection and the internal radius of the spring at the angle neutralposition; β′: angle between the angle null direction and the directionof the external radius of the spring at the angle neutral position. Inthis case, it should be noted that the angle difference (α′−β′) is aconstant which is governed by the geometry of the spring and theorientation of the spring end surface 222. The angles α and β correspondto the corresponding angles relating to the internal radius and externalradius, respectively, during the measurement of the distance measure Y.The formulae in FIG. 7 show the way in which the sought arc measure b isderived from measured variables.

If the arc measure b has now been determined in the described way, or insome other way, then the remaining distance which actually still has tobe moved through is calculated by subtracting the arc measure determinedby measurement, or the wire length associated with it, from thefictitious remaining distance associated with the fictitious endposition 222-1. Once the remaining distance has been determined, then acorresponding NC set is produced in the control system, and the wirefeed feeds the wire through the calculated remaining distance. Theconstant final section is then also moved through, as a result of whichthe end surface 222 of the finished spring is located with highprecision in the area of the nominal position of the spring end.

The feed through the remaining distance is carried out in a creepingprocess, that is to say it is carried out at a reduced feed rate. Thecreeping process is also used for the feed in the subsequent constantfinal section, until the entire length of the spring has been produced.This situation is illustrated schematically in FIG. 3 by turns in theform of dashed lines and in an enlarged form in FIG. 5. The field ofview 262 of the second camera is sufficiently great that the spring endsection with the spring end is within the field of view both for theintermediate measurement as described above (to determine the distancemeasure Y) and in the final position with the complete spring. In theexample shown in FIG. 5, the second camera is used to carry out ameasurement of the overall length of the finished spring. A secondmeasurement area 266 is generated for this purpose, which represents asecond measurement tool by means of which the longitudinal distance,identified by the arrow Z, between a measurement point 270 on the endface of the spring and the left-hand edge of the measurement tool 266can be determined. The edge of this measurement window is in this caseused as a “fixed stop” for the measurement, that is to say as areference element whose coordinates with respect to a machine coordinatesystem of the spring winding machine are known or can be determined. Theoverall length of the spring can be measured absolutely and precisely inthis way on the basis of the distance value Z.

The determination of the spring end position as explained in conjunctionwith FIGS. 3 and 4 can be used to further control the manufacturingprocess. In this case, it should be noted that the wire feed, that is tosay the feed device, in general operates very precisely andsubstantially without slip, as a result of which the wire length fed bythe feed device corresponds to a good approximation to the wire lengthpredetermined by the machine program. If the measurements of the springend position now show a tendency for the spring end position (angleposition of the spring end after completion of the winding process) tobe systematically less than expected or greater than expected, then thiscan indicate that the spring diameter has a tendency to be smaller thanintended or larger than intended, respectively since, for example, witha larger diameter and the same wire length, an angle position of thespring end can be expected which is less than the desired nominal angleposition. The evaluation system has an evaluation algorithm whichidentifies such tendencies in the measured positions of the spring endand feeds this information back to the control system, thus allowing thecontrol system to implement an appropriate diameter correction, byadjusting the position of the winding pins, for the manufacture of thenext springs. The measurement of the spring end position therefore alsoindirectly provides a determination of the spring diameter, and acorrection option based on this.

The above description is directed to representative examples. From thedisclosure given, those skilled in the art will not only understand ourmethods, apparatus and their attendant advantages, but will also findapparent various changes and modifications to the structures and methodsdisclosed. It is sought, therefore, to cover all changes andmodifications as fall within the spirit and scope of this disclosure, asdefined by the appended claims, and equivalents thereof.

1. A method of producing helical springs by spring winding with anumerically controlled spring winding machine comprising: feeding a wirecontrolled by an NC control program through a feed device to a formingdevice; forming the wire into a helical spring in the forming device;defining a measurement time which occurs in a final phase of an overallmanufacturing time for the helical spring at a time period before theend of the overall manufacturing time; measuring a position of a springend formed by an end surface of the wire to determine an actual angleposition of the spring end at the measurement time; determining aremaining distance for the wire feed required to achieve a nominal angleposition of the spring end, as intended for the helical spring, at apredefined reference time which occurs at a time after the measurementtime; and feeding the wire through the remaining distance.
 2. The methodaccording to claim 1, wherein the reference time corresponds to the endof the overall manufacturing time.
 3. The method according to claim 2,wherein an opposite spring end is produced immediately after reachingthe reference time by separating the helical spring which has beenproduced from the fed wire.
 4. The method according to claim 1, whereinthe reference time is an intermediate time which occurs at a time beforethe end of the overall manufacturing time, wherein, after passagethrough the remaining distance, a predefined final part of themanufacturing time passes to the end of the overall manufacturing time,and the helical spring which has been produced is then separated fromthe fed wire.
 5. The method according to claim 1, wherein a camera witha two-dimensional field of view measures the position of the spring end,and the camera is arranged such that an end section of the helicalspring with the spring end lies within a field of view at themeasurement time.
 6. The method according to claim 5, wherein the camerais arranged alongside a path of the helical spring such that anobservation direction is aligned transversely to a longitudinaldirection of the helical spring.
 7. The method according to claim 6,wherein the actual angle position of the spring end is determined fromdata from the field of view by determining a distance value for adistance, which is measured transversely to a longitudinal axis of thehelical spring, between a tangent to an external contour of a turn on acircumference of the helical spring and a projection of the spring endin the field of view.
 8. The method according to one claim 1, wherein arelative orientation of the spring end is determined at the measurementtime with respect to an observation direction, and the measured distancevalue is corrected as a function of the orientation.
 9. The methodaccording to claim 1, wherein the measurement time is selected as afunction of geometric data of the helical spring such that, in aremaining time interval required to move through the remaining distance,at least one turn of the helical spring is produced.
 10. The methodaccording to claim 1, wherein a feed movement of the wire is interruptedto carry out measuring the position of the spring end.
 11. The methodaccording to claim 1, wherein at least one further measurement iscarried out after the end of the overall manufacturing time and beforecutting off the helical spring from the wire fed through the feeddevice.
 12. The method according to claim 11, wherein an overall lengthof the finished helical spring is determined on the basis of the furthermeasurement.
 13. A spring winding machine that produces helical springsby spring winding under the control of an NC control program accordingto the method of claim 1 comprising: a feed device; and a forming devicethat receives wire from the feed device and comprises at least onewinding tool which controls the diameter of the helical spring at apredeterminable position, and at least one pitch tool whose action on ahelical spring being produced controls a local pitch of the helicalspring.
 14. The spring winding machine according to claim 13, furthercomprising a camera positioned at a distance from the forming devicesuch that a free spring end section runs into a field of view of thecamera in a final phase of production of the helical spring.
 15. Acomputer program product stored on a computer-readable medium or in theform of a signal, wherein the computer program product results in thecomputer carrying out the method according to claim 1 when the computerprogram product is loaded in the memory of a computer and is run by acomputer of a spring winding machine.